Bad governor or air drier?

How fast truck loosing air pressure?

 

Doesn't take much of an air leak. My fan hub went bad and started pissing air right after I had a new dryer put on. I thought for sure it was the new dryer that was bad until I heard the air coming out of the fan hub.

 

It could be the braided steel signal line from the air governor to the air dryer, inside the steel braid is a plastic air line that gets brittle with age.

Just moving it a few inches can crack the line inside causing a big air leak.

 

Sounds to me like your air leak is between you air dryer, Governor, and compressor. Depending on where your Governor is mounted (on trucks today, this is usually on the air drier) either way there is a 1/4” line that runs from the air drier to the compressor unloader valve. If it leaks your air system will act like the way you describe.

 

The unloader on the air compressor. There was a good thread on this problem about a month ago.

 

i had same annoying problem on my peterbilt with ad9. Changed unloader and didnt fix it. i decided to put new governor on. cheap 20 part and easy to install. That fixed the problem and now doesnt sneeze for like 5 or more minutes

 

Sounds like youve got a decent leak in your air system. Acceptable air system leaks are generally 2 psi over 2 mins. Your gouvernor is usually set to cut out the compressor at 135psi. In order fir the compressor to kick back in, air pressure needs to drop below 115 psi. Therefore if your gouvernor cuts out at its cutout pressure its not your gouvernor. If you can build up system pressure, its not your compressor.
Bad gouvernor= system will build up safety release valve pressure. Sounds like a machine gun firing.
Bad compressor= not able to build up air pressure.

System test. Build up system pressure and turn off the vehicle.watch your gauge for around 2 mins. If it falls more than 2 psi the air leak you mentioned or another is causing your problem.
Im generalizing the specs just to say.

Thats my guess.

 

Mine was popping off every 25 sec. Was leaking at the purge valve on the air dryer, replaced the whole unit all was good.